Facial bones:Mandible
The mandible consists of a curved, horizontal portion, the body, and two perpendicular portions, the rami, which unite with the ends of the body nearly at right angles (angle of the jaw). It articulates with both temporal bones at the mandibular fossa at the temporomandibular joints (TMJ). Body The body of the mandible is curved, somewhat like a horseshoe, and two surface and two borders: * external surface ** midline ridge indicating the symphysis ** The external oblique ridge is the continuation of the anterior margin of the ramus (attachment of buccinator) ** mental foramen - inferior to second premolar tooth, midway between the superior and inferior borders; allows for the passage of the mental vessels and mental nerve ** Attachments: platysma and investing layer of the deep cervical fascia. * internal surface ** concave from side-to-side ** The mylohyoid line passes fowards and downwards, from the below the third molar tooth. This gives attachment to the mylohyoid muscle. Above this line, anteriorly is the sublinguinal fossa housing the sublingual gland. Below this line posteriorly, is the submandibular fossa housing the superficial portion of the submandibular gland. ** In the midline, there are four small projections called mental spine, for attachment of genioglossus and geniohyoid. Diagastric fossa, two oval depression, on either side of the midline gives attachment fo r the anterior bellies of hte digastric muscle. ** The pterygomandibular raphe attached below the last molar tooth. * superior (or alveolar) border ** wider behind than in front ** The surface is projected up as alveolar bone to form hollows for the teeth (normally 16). These gives attachment to the periodontal ligament. ** attachment of buccinator muscle. * inferior border ** rounded, longer than the superior border and thicker in front than behind ** The lower border is crossed by the facial artery and the mandibular branch of the facial nerve Ramus The ramus is quadrilateral in shape, and has two surfaces, four borders, and two processes and one canal: * external (or lateral) surface. Flat; gives attachment to the masseter muscle. * inner (or medial) surface ** mandibular foramen located half way between the anterior and posterior borders of ramus. The inferior alveolar vessels and nerve pass into this. ** Lingula mandible - prominent, sharp bony ridge in front of the mandibular foramen; gives attachment to the sphenomandibular ligament. * lower border ** thick, straight and continuous with the inferior border of the body of the mandible * posterior border ** thick, smooth, rounded and covered by the parotid gland. ** Angle of the mandible is at its junction of the posterior border and the body. It projects upwards as the neck and expands into the head of the mandible. It is the attachment for medial pterygoid. * anterior border ** thin above and thicker below; continuous down as the oblique line and up to the coronoid process. * upper border: consists of the coronoid process anteriorly and '''condylar process '''posteriorly separated by the mandibular notch. The mandibular canal runs obliquely downward and forward in the ramus, and then horizontally forward in the body, where it is placed under the alveoli and communicates with them by small openings. On arriving at the incisor teeth, it turns back to communicate with the mental foramen, giving off two small canals which run to the cavities containing the incisor teeth. It contains the inferior alveolar vessels and nerve, from which branches are distributed to the teeth via the incisive nerve. Coronoid Process * thin, triangular eminence from the upper border of the ramus of the mandible * separated from the condylar process posteriorly by the mandibular notch * temporalis muscle insert into lts medial and lateral surfaces * masseter muscle also inserts to its lateral surface * temporalis muscle also inserts to its medial surface Condylar Process * thicker than the coronoid process. It is convex anteroposteriorly and side to side, and extends farther on the posterior than on the anterior surface * consists of two portions - condyle and neck * condylar neck is flattened from front to back; lateral pterygoid muscle inserts into it on the pterygoid fovea. Posteriorly the TMJ joint capsule is attached. The auriculoptemporal nerve and maxillary artery and vein cross the medial aspect of the neck, lying between it and the sphenomandibular ligament. * The condyle is marked convex and projects beyond the neck with articular surface for articulation with the articular disk of the temporomandibular joint (TMJ) Blood supply * facial artery (branch of external carotid artery) * lingual artery (branch of external carotid artery) * inferior alveolar artery (branch of maxillary artery)